The Nyon Arrangement was a short multilateral agreement signed on 14 September 1937 at Nyon, Switzerland, by nine states: the United Kingdom, France, the Soviet Union, Bulgaria, Egypt, Greece, Romania, Turkey, and Yugoslavia. It responded to a wave of submarine attacks on neutral merchant shipping in the Mediterranean during the Spanish Civil War — attacks widely attributed to Italian submarines operating in support of Franco's Nationalists, though Italy was not named in the text, which referred only to "piratical acts by submarines."
The arrangement authorised British and French naval forces to patrol designated Mediterranean zones and to attack any submarine that assaulted a non-Spanish merchant vessel, or that was encountered in circumstances suggesting it had just done so or was about to. A supplementary agreement signed at Geneva on 17 September 1937 extended the same regime to surface vessels and aircraft.
Several features made Nyon notable in interwar diplomacy:
- It was negotiated and concluded in roughly ten days, an unusually rapid pace for collective-security instruments of the period.
- It bypassed the League of Nations machinery, which had proved ineffective on Spain, while still framing the response in collective terms.
- Italy and Germany were invited but did not attend; Italy joined the patrol scheme shortly afterward, in effect policing attacks it had itself been carrying out.
- It treated the attacking submarines as pirates under international law, sidestepping the politically charged question of belligerent rights in the Spanish conflict.
Submarine attacks against neutral shipping in the Mediterranean essentially ceased after the patrols began. Anthony Eden, then British Foreign Secretary, considered it one of the clearer diplomatic successes of his tenure. Historians often cite Nyon as a rare instance in the late 1930s where Britain and France acted decisively against Axis-aligned aggression, in contrast to the broader pattern of appeasement that would culminate in Munich a year later. The arrangement is also frequently referenced in discussions of how the international law of piracy can be adapted to state-sponsored maritime violence.
Example
In September 1937, after Italian submarines repeatedly torpedoed neutral merchant ships, nine states meeting at Nyon agreed to let British and French warships sink any submarine attacking non-Spanish vessels in the Mediterranean.